As is well known in the mining industry, there are numerous apparatus and methods used in rock bolting for strata control. An internationally accepted method of strata control is full column resin bolting which provides rapid and effective strata control at relatively lower cost than traditional external set supports.
Resin-anchored cable bolts are generally defined as “active methods” of support. These active reinforcing methods are intended to react to rock mass movement, develop a restraining force and transfer that force back to the rock mass. This counteracts the driving force and eventually results in a balanced condition when the total mobilized resistance within the rock mass is at least equal to the available driving force.
Resin anchored cable bolts can be installed as either passive or post-tensioned supports. In tensioning applications, standard cable heads, low-profile heads, barrels and wedges, can be used to tension the cable.
Typically, resin anchored cable bolts require a borehole to be drilled in the mine surface, such as a roof or wall. A resin cartridge is inserted into the borehole and then the cable bolt is inserted and rotated to rupture the resin cartridge. The cable bolt will typically have a roof plate mounted upon the cable bolt, a barrel and wedge assembly mounted to the end of the cable bolt and a drive head, typically a nut, that can be rotated with typical mine roof bolt installation equipment. The nut is rotated to drive the barrel and wedge assembly against the roof plate and mine surface to tension the cable.
U.S. Pat. No. 6,074,134 discloses an example of cable bolt assembly.
One disadvantage of the cable bolt of the '134 patent is that the cable twists during tensioning. It has been found to be advantageous to restrain twisting of the cable bolt during tensioning. When tensioning a steel cable, it is not uncommon for the cable itself to twist between the point of application of torque for tensioning and the point at which the cable is cemented in place. This can cause a decrease in the length of the cable. Upon release of the drive equipment, the cable can untwist thereby returning to its longer length and causing an undesirable decrease in the tension on the cable.
Another problem with this cable bolt assembly is that the barrel and wedge assembly is fairly large and extends into the mine area, which can be a problem in small spaces where space is at a premium. Additionally, the barrel and wedge assemblies are costly to manufacture and adds cost to the cable bolt.
U.S. Pat. No. 8,033,760 discloses another example of a resin anchored cable bolt. As stated in the abstract, a tensioning assembly 10 for a cable bolt 11 comprises a clamping device (14, 16) adapted for fastening to the bolt and an outer member 18 adapted for interacting with the clamping device. The outer member 18 is able to undergo relative movement with respect to the clamping device in the direction of the bolt's axis, and under such movement, the clamping device is caused to fasten to the bolt. Furthermore, the outer member is adapted for interacting with the bolt 11 whereby, during such relative movement, twisting of the bolt 11 with respect to the outer member 18 is restrained.
A problem with this cable bolt assembly is the complexity of the clamping device and the outer member. This adds cost to the cable bolt assembly. Also, the clamping device and outer member is large and extends into the mine area, which can be a problem in small spaces where space is at a premium.
Australian patent application 2008100948 discloses a cable bolt assembly that includes a tensioning device having a strata plate, a barrel fitting for attaching a cable and a barrel actuator. The tensioning device includes an engaging means for interlocking the barrel fitting and the strata plate to prevent rotation of the barrel fitting and the cable relative to the strata plate. The locking means is disclosed to be a pin or rod configured for engagement with a mating hole in the barrel fitting. In an alternative embodiment, the locking means may be an adhesive. In the preferred embodiment, the pin or rod is in the form of a shear pin designed to break or fracture at a predetermined load to them permit longitudinal movement of the barrel actuator relative to the barrel fitting. The barrel fitting also includes a thrust bearing configured to engage a domed washer to prevent rotational movement while permitting relative longitudinal movement.
This cable bolt assembly suffers from the same disadvantages as the previously discussed cable bolt assemblies.
U.S. Pat. No. 7,625,155 discloses a cable bolt assembly which includes tension cylinders and tension nuts, alone or in combination with cables and roof bearing plates, for use in underground mines to support mine roofs. The cables have a first end that is secured within a borehole in a roof, a second end for exposure from the borehole, and a weight bearing nut secured to the second end. The tension cylinder accommodates, yet is not affixed to, the cable, and includes a threaded exterior surface and an interior cable-accommodating channel. The tension nut has a threaded interior surface complementary to the threaded exterior surface of the tension cylinder, and is rotatable about the tension cylinder. The assembly with the cable and roof bearing plate are positioned within the borehole so that the tension cylinder is within and extends beyond the aperture of the roof bearing plate, and rests against the weight bearing nut of the cable. As the tension nut is rotated about the tension cylinder, and until the nut has compressed the roof bearing plate against the mine roof, the cable does not rotate or twist.
One of the problems with the '155 system is the requirement that the weight bearing nut be secured to the end of the cable. It is not disclosed in the patent the method of attaching the weight bearing nut, but it would seem to require either welding or the use of a barrel and wedge assembly. Regardless, there is added cost to the system. Additionally, if welded, the tension cylinder, tension nut and roof bearing plate has to be pre-assembled on the cable bolt. This adds to shipping costs and handling problems. Also, as with previous systems, the cable bolt of the '155 patent is large and extends into the mine area, taking up valuable space.
United States Application 20090191007 discloses a mixing and tensioning assembly having a cable bolt, an integral body of a wedge barrel and threaded sleeve disposed about the cable bolt, a nut disposed along the integral body and a bearing plate. While the preferred embodiment contemplates the integral body being a continual unitary member, a person of skill in the art would recognize that other embodiments would contemplate an interface between a wedge barrel and a threaded sleeve achieved via a weld between a wedge barrel and a threaded sleeve, via a recessed barrel with a mating surface corresponding to a mating end of a threaded sleeve, via screwing the threaded sleeve into the wedge barrel, or via prongs on one end of the threaded sleeve engaging apertures in the wedge barrel, all to fix the interrelationship between the wedge barrel and the threaded sleeve. The result in all embodiments is an interdependent wedge barrel and threaded sleeve which when either part is acted upon by a force the same or substantially similar force is also transmitted to the other part of the integral body.
There are also opposing and mating shapes in the aperture of the bearing plate and the threaded member to permit the threaded member to slide through the aperture of the plate but also reduce or prevent the threaded member from spinning within the aperture of the bearing plate.
The cable bolt assembly of United States Application 20090191007 has the same disadvantages of the previous cable bolt assemblies, in that it employs a typical wedge and barrel assembly to engage and hold the cable. The wedge and barrel assembly is fairly large and extends into the mine area, which can be a problem in small spaces where space is at a premium. Still further, the barrel and wedge assemblies are costly to manufacture and adds cost to the cable bolt. Additionally, the nut, washers and plate have to be assembled on the integral body prior to the integral body being inserted over the cable. This increases the labor required to install the cable bolt.